1. Field of the Invention
The invention relates to the fabrication of integrated circuits, and in particular to a method of improving the deposition of materials during the fabrication of integrated circuits by adjusting a physical property of a precursor liquid.
2. Statement of the Problem
The manufacture of integrated circuits entails series of numerous steps in which thin layers of materials are sequentially deposited, patterned and etched to form the various components of the circuit. Therefore, to utilize a material in an integrated circuit it is necessary to be able to make a high quality thin film of the material. It is essential that the quality must be high not just from a macroscopic viewpoint, but, since the individual components of an integrated circuit are microscopic, the film must also be of high quality when examined on the microscopic level.
One of the problems associated with integrated circuit manufacture is that it is difficult to make high quality thin films of some materials, particularly complex materials such as layered superlattice materials. Often the best methods known to make these materials are complex, inefficient or unreliable. Also, the methods of deposition of various materials vary, and this lack of uniformity causes interruptions and inefficiency in the overall manufacturing process.
One category of common deposition methods is liquid deposition, in which a precursor liquid of the material to be deposited is applied to an underlying substrate. The precursor may be a simple solution of the material to be deposited dissolved in a solvent. More typically, the precursor is a solution of one or more chemical precursor species that are reacted on the substrate after the precursor liquid is applied. After a coating of precursor liquid has been applied, it is usually treated to form a solid layer of desired material.
In general, the quality of the deposited solid layer of material depends, among other factors, on the properties of the liquid coating of precursor. Some of the many properties of the liquid coating that influence the integrated circuit manufacturing include: the concentration of material or chemical precursor species in the liquid coating; the thickness of the liquid coating; and the coverage of the underlying substrate by the liquid coating. For example, usually good step coverage of a substrate by an overlying solid layer is desired. At the same time, it is often important for the deposited solid layer of material to fill all the depressions and steps in the underlying substrate and present a uniformly smooth and planar surface. In current manufacturing processes the combination of good step coverage and a smooth planar surface are achieved by using a chemical mechanical polishing (xe2x80x9cCMPxe2x80x9d) process step after formation of the solid film. This can be the source of problems in the manufacturing process because the CMP step not only adds to the complexity and expense of the manufacturing process, but it also causes particle formation. Particles formed in the CMP process are difficult to entirely remove and can seriously degrade the integrated circuit. A related problem in current manufacturing processes is that some otherwise practical deposition methods cannot be used to deposit layers of certain solid materials because the ensuing CMP process leads to insurmountable problems.
The quality of the applied precursor liquid coating and the resulting layer of solid material are also influenced by the deposition method and conditions. For example, if a misted deposition method is used to apply the coating of precursor liquid, the flow rate of mist and the particle size of the mist influence the qualities of the liquid coating. At the same time, the physical qualities of the precursor liquid influence the efficacy of a given deposition apparatus to apply a liquid coating of desired qualities on the substrate. A problem in current manufacturing methods is that otherwise practical deposition methods cannot be used to deposit layers of certain materials because the quality of the precursor liquid is not suitable for operation with a given type of deposition apparatus.
3. Solution to the Problem
The invention solves the problems by selectively and systematically adjusting the physical properties of the precursor liquids to replace one or more conventional integrated circuit processing steps. In one preferred embodiment, the viscosity or other related physical property is selected so that the precursor fills depressions in the substrate and at the same time provides a smooth planar surface, thereby eliminating the need for a CMP process. In another embodiment a first precursor having a first viscosity or other related physical property is deposited followed by the deposition of a second precursor having a second viscosity or other related physical property. In this embodiment, preferably both the first and second precursors are precursors for forming essentially the same predetermined material.
The invention also solves the above problems by providing a method of fabricating a thin film of a solid material in which a physical property of a liquid precursor is changed during the step of depositing the precursor on a substrate. The physical property can be changed in steps or continuously. The liquid precursor can be dried between the changing steps or only after both the original precursor and the changed precursor are applied.
The invention also solves the above problems by providing an apparatus for forming a thin film of a solid material having two liquid sources and a means for mixing the two liquids in a continuous and controlled manner just prior to the step of depositing the liquids.
The invention provides a method of fabricating a thin film of solid material having a planarized thin film surface, the method comprising steps of: providing a substrate having a substrate surface including non-planarized areas; providing a precursor liquid for forming the layer of solid material, the precursor liquid having a viscosity of 5 centipoise or less; applying the precursor liquid to the substrate; and treating the precursor liquid on the substrate to form the thin film of solid material having the planarized thin film surface. Preferably, the viscosity does not exceed 2 centipoise, and most preferably the viscosity is between 1 centipoise and 2 centipoise. Preferably, the thin film of solid material comprises a metal oxide, such as a layered superlattice material, silicon dioxide, or a silicon glass. Preferably, the precursor liquid includes a compound selected from the group consisting of alkoxides, carboxylates, and combinations thereof. Preferably, the precursor includes a metal compound, and preferably the metal compound is selected from the group consisting of metal 2-ethylhexanoates and metal 2-methoxyethoxides. Preferably, the precursor liquid comprises a solvent and the solvent is selected from the group consisting of alcohols, aromatic hydrocarbons, and esters. Preferably, the step of applying comprises spin-coating a thin film of the precursor liquid on the substrate. Alternatively, the step of providing a substrate comprises placing a substrate inside an enclosed deposition chamber; and the step of applying comprises the steps of: producing a mist of the precursor liquid, and flowing the mist through the deposition chamber to form the precursor liquid on the substrate.
The invention also provides a method of fabricating a thin film of solid material comprising steps of: providing a substrate and a precursor liquid suitable for forming a thin film of the solid material upon application to a substrate and treatment; applying the precursor liquid to the substrate; changing a physical property of the precursor liquid subsequent to the step of applying; subsequent to the step of changing, continuing to apply to the substrate the precursor liquid having the changed physical property; and treating the precursor liquid on the substrate surface to form the thin film of solid material. Preferably, the method further includes the step of drying the precursor liquid on the substrate between the steps of applying and continuing to apply. Preferably, the steps of changing and continuing to apply are repeated at least once. Preferably, the step of changing is performed at the same time as the step of continuing to apply. Preferably, the step of changing is performed continuously for a predetermined time. Preferably, the physical property is viscosity, the surface tension between the precursor liquid and the substrate surface, density, heat capacity, the heat of vaporization, or vapor pressure.
In a further aspect, the invention also provides a method of fabricating a thin film of solid material comprising the steps of: providing a substrate; providing a precursor liquid; adjusting a physical property of the precursor liquid while applying the precursor liquid to the substrate; and treating the precursor liquid on the substrate surface to form the thin film of solid material.
In another aspect, the invention provides a method of fabricating a thin film of solid material comprising steps of: providing a substrate, a first liquid, and a second liquid; flowing the first liquid through a first fluid flow controller and the second liquid through a second fluid flow controller; mixing the first liquid with the second liquid in amounts determined by the first and second fluid flow controllers to form a precursor liquid; applying the precursor liquid to the substrate; and treating the precursor liquid on the substrate surface to form the thin film of solid material. Preferably, the method further includes the step of adjusting the first fluid flow controller to change the flow of the first liquid through the first fluid flow controller during the step of applying. Preferably, the at least one of the fluid flow controllers is a volumetric flowrate controller. Preferably, the thin film of solid material comprises a metal oxide, such as a layered superlattice material, silicon dioxide, or a silicon glass. Preferably, the precursor includes any of the compounds and solvents mentioned above. Preferably, the step of treating comprises a process selected from the group consisting of: exposing to vacuum, exposing to ultraviolet (UV) and/or infrared (IR) radiation, electrical poling, drying, heating, baking, rapid thermal processing, and annealing.
The invention also provides apparatus for fabricating a thin film of solid material, the apparatus comprising: a source of a first liquid, a source of a second liquid, and a mist generator; a first volumetric flowrate controller connected between the source of a first liquid and the mist generator and a second volumetric flowrate controller connected between the source of a second liquid and the mist generator; a deposition chamber in fluidic communication with the mist generator; and an exhaust assembly in fluidic communication with the deposition chamber. Preferably, the apparatus further includes a mixing chamber between the volumetric flowrate controllers and the mist generator. Preferably, the first liquid is a solvent and the second liquid is a compound selected from the group consisting of alkoxides, carboxylates, and combinations thereof.
The invention not only permits relatively simple changes in deposition parameters to replace relatively complex conventional integrated fabrication process, but results in integrated circuit materials having better electrical properties. Preferably, the variations from flatness of the surface of a thin film made according to the invention, prior to patterning, are 5% or less of the total thickness of the layer. Most preferably, the variations from flatness are 3% or less of the total thickness, and in routine uses of the invention there often are no variations more than 1% of the total thickness. Numerous other features, objects and advantages of the invention will become apparent from the following description when read in conjunction with the accompanying drawings.